^{1}, Xiao-Hong Yan

^{1,2,a)}and Yang Xiao

^{1}

### Abstract

Controlling a spin current by electrical means and eliminating the use of ferromagnetic contacts becomes a focus of research in spintronics, as compared with conventional magnetic control methods, electrical one could reduce the dimensions and energy consumption of integrated devices. Inspired by recent progress of controlling the hydrogenation on graphene [Xie et al., Appl. Phys. Lett. 98, 193113 (2011)], we investigate the electronic structure and spin-current transport of partially hydrogenated zigzag graphene nanoribbon (ZGNR) with various hydrogenation geometries, through first-principles calculations. It is found that for ZGNR in ferromagnetic edge-coupling state, near-edge hydrogenation would suppress the magnetization on the edge of ZGNR, and lower down the transmission around EF to zero except two peaks, which reside discretely on both sides of EF with opposite spins. Based on this feature, we propose and demonstrate a three-terminal device, where the spin polarization of the current can be modulated by gate voltage (Vg ) to vary from (almost) 100% to −100%, which could serve as a perfect electrically-controlled “pure-carbon” dual-spin filter. Especially, the spin polarization varies gradually with Vg , so a current with any ratio of spin-up to spin-down electron numbers can be achieved. Moreover, the influences of ZGNR width and hydrogenation-region length on the system's performance are also discussed and a large range of ZGNR configurations are found to be suitable for the application of such a device.

This work is supported by the National Natural Science Foundation of China (NSFC10874089 and NSFC51032002), the key project of National High Technology Research and Development Program of China (2011AA050526), the Funding of Jiangsu Innovation Program for Graduate Education (CXZZ11_0190), and the Fundamental Research Funds for the Central Universities (NS2012005 and NS2012064).

I. INTRODUCTION

II. COMPUTATIONAL METHOD

III. RESULTS AND DISCUSSIONS

IV. CONCLUSION

### Key Topics

- Electric currents
- 14.0
- Graphene
- 13.0
- Polarization
- 9.0
- Carbon
- 7.0
- Ferromagnetism
- 7.0

##### H01F1/00

## Figures

(a) Schematic illustration of two-terminal device constructed by infinite 5-ZGNR. (b)–(d) The corresponding spin-dependent bandstructure, density of states, and transmission spectrum for 5-ZGNR in FM state, respectively. The zero of energy is set to be the Fermi level, which is defined as the average of the Fermi levels of the two leads.

(a) Schematic illustration of two-terminal device constructed by infinite 5-ZGNR. (b)–(d) The corresponding spin-dependent bandstructure, density of states, and transmission spectrum for 5-ZGNR in FM state, respectively. The zero of energy is set to be the Fermi level, which is defined as the average of the Fermi levels of the two leads.

(a)–(h) Spin-dependent electronic transmission spectra for (a) bare and (b)–(h) partially hydrogenated 5-ZGNRs with different hydrogenation geometries. The left and right panels show the corresponding configurations and their isovalue surfaces of the spin charge density magnetization (i.e., up-spin charge density minus down-spin charge density). Red (dark) and blue (light) represent positive (spin-up polarized) and negative (spin-down polarized) values, respectively, with the isovalue of . The isovalue surfaces exhibit spherical geometries around atoms, where large size indicates large magnetization (near-edge atoms) and small size indicates small magnetization (inner atoms). For clarity, balls for atoms are not shown, and the shaded region is passivated by hydrogen atoms. (i) Take the configuration in (h) as an example to show the structural optimization. The scattering region shown in (i) is considered to be a periodic configuration for optimization, and the unit cell is shown by the gray and solid box. During the optimization, the atoms outside the red and dashed box are frozen, meanwhile, the atoms within that box (including the shaded region) are fully relaxed until all the forces are less than 0.02 eV/Å. This would stabilize the whole hydrogenation area (shaded region), including its edges. After optimization, the left and right sides of the scattering region are contacted with semi-infinite GNR electrodes to calculate the transport properties. (j) The three-dimensional and enlarged views of the configuration in (h).

(a)–(h) Spin-dependent electronic transmission spectra for (a) bare and (b)–(h) partially hydrogenated 5-ZGNRs with different hydrogenation geometries. The left and right panels show the corresponding configurations and their isovalue surfaces of the spin charge density magnetization (i.e., up-spin charge density minus down-spin charge density). Red (dark) and blue (light) represent positive (spin-up polarized) and negative (spin-down polarized) values, respectively, with the isovalue of . The isovalue surfaces exhibit spherical geometries around atoms, where large size indicates large magnetization (near-edge atoms) and small size indicates small magnetization (inner atoms). For clarity, balls for atoms are not shown, and the shaded region is passivated by hydrogen atoms. (i) Take the configuration in (h) as an example to show the structural optimization. The scattering region shown in (i) is considered to be a periodic configuration for optimization, and the unit cell is shown by the gray and solid box. During the optimization, the atoms outside the red and dashed box are frozen, meanwhile, the atoms within that box (including the shaded region) are fully relaxed until all the forces are less than 0.02 eV/Å. This would stabilize the whole hydrogenation area (shaded region), including its edges. After optimization, the left and right sides of the scattering region are contacted with semi-infinite GNR electrodes to calculate the transport properties. (j) The three-dimensional and enlarged views of the configuration in (h).

Left and right panels show the structures of 5-ZGNRs with two different hydrogenation geometries [(a) and (b)], corresponding spin charge density magnetizations [(c) and (d)] and transmission spectra [(e) and (f)].

Left and right panels show the structures of 5-ZGNRs with two different hydrogenation geometries [(a) and (b)], corresponding spin charge density magnetizations [(c) and (d)] and transmission spectra [(e) and (f)].

(a) Schematic illustration (top and side views) of three-terminal ZGNR device with rectangular hydrogenation in FM state. The carbon atoms within the middle shaded region are passivated by hydrogen atoms. (b)–(d) The corresponding spin-dependent transmission spectra for , 0.8, and −0.8 V, respectively.

(a) Schematic illustration (top and side views) of three-terminal ZGNR device with rectangular hydrogenation in FM state. The carbon atoms within the middle shaded region are passivated by hydrogen atoms. (b)–(d) The corresponding spin-dependent transmission spectra for , 0.8, and −0.8 V, respectively.

(a) The spin-dependent currents under bias of 10 mV between left and right leads vary with Vg for the device shown in Fig. 4 . (b) The corresponding spin polarization of the current varies with Vg .

(a) The spin-dependent currents under bias of 10 mV between left and right leads vary with Vg for the device shown in Fig. 4 . (b) The corresponding spin polarization of the current varies with Vg .

The spin-dependent transmission spectra for two-terminal N-ZGNR device with different widths (N) and different hydrogenation geometries. Left and right panels give out corresponding structures [only the scattering region is shown, and its left and right are connected with semi-infinite bare ZGNRs like Fig. 1(a) ]. The carbon atoms within the shaded region are passivated by hydrogen atoms. (a)–(d) for N = 5, (e)–(g) for N = 4, and (h)–(j) for N = 6, 7, and 8, respectively.

The spin-dependent transmission spectra for two-terminal N-ZGNR device with different widths (N) and different hydrogenation geometries. Left and right panels give out corresponding structures [only the scattering region is shown, and its left and right are connected with semi-infinite bare ZGNRs like Fig. 1(a) ]. The carbon atoms within the shaded region are passivated by hydrogen atoms. (a)–(d) for N = 5, (e)–(g) for N = 4, and (h)–(j) for N = 6, 7, and 8, respectively.

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